Air cooled microwave cooking oven and door

ABSTRACT

In a microwave cooking apparatus, more particularly in an apparatus having a radiant heating means for surface browning of the foodstuff and the like, the interior of the door and the handle are heated at a relatively high temperature. A blower means for providing an air stream is so installed as to cool the interior of the door whereby prevents the temperature rise of the door and the handle due to the heat from the browning means and so forth.

United States Patent 1191 Tateda 1 Jan. 1, 1974 [54] AIR C OOLEDMICROWAVE COOKING 2,525,614 10/1950 Nelson et a1 126/21 A OVEN AND DOOR3.057341 10/1962 Perl 126/21 R 3,081,392 3/1963 Warner.... 219 391 [7Inventor! Koichi Tateda, Osaka, Japan 3.679.855 7/1972 Blinzer 1 1 2191055 3.681.557 8/1972 Suzuki et all 219/1055 [73] Assgnee' SharpKabush'k' Osaka 3,711,673 1/1973 Takeda et a1... 1. 219/1055 Japan3,509,868 5/1970 Mono 126/198 [22] Filed: Nov. 8, 1971 1 PrimaryExaminer-Thomas J. Kozma [2]] Appl' 1961591 Assistant Examiner-Hugh D.Jaeger Att0rneyFlehr, Hohbach, Test, Albritton & Herbert [30] ForeignApplication Priority Data Nov. 11, 1970 Japan .45/100487 [57] ABSTRACTNov. 11, 1970 Japan 45/100489 In a microwave cooking apparatus, moreparticularly in an apparatus having a radiant heating means for [52] US.Cl. 219/10.55, 126/198 surface browning of the foodstuff and the like,the in- [51 Int. Cl. 1105b 9/06 terior of the door and the handle areheated at a rela- [58] Field of Search 126/21 A, 21 R, 39 C, tively hightemperature. A blower'means for providing 126/198, 273 R; 219/391, 10.55an air stream is so installed as to;coo1 the interior of g the doorwhereby prevents the temperature rise of the {56] References Cited doorand the handle due to the heat from the brown- UNlTED STATES PATENTS mgmeans and SO forth- 2,438,035 4 Claims, 3 Drawing Figures 3/1948 Buhmanet'al 126/39 C PAIENTEn'JAn 1 m4 3783219 sum 2 or 2 Fig.3

INVENTOR.

Koichi Tafe da A'Ws AIR COOLED MICROWAVE COOKING OVEN AND DOORBACKGROUND OF THE INVENTION This invention relates to a cookingapparatus using electricity, gas, hot blast and the like as the heatsource thereof, and more particularly to an improved cooking apparatusin which the cooling unit is provided to maintain the whole of theapparatus at a comparatively low temperature of safety.

The cooking apparatus, in general, use electricity, gas, hot blast andso forth as the energy source thereof. These energies are supplied tothe interior of the oven compartment, wherein the foodstuff and the likeabsorb these energies and thereby the foodstuff is cooked. Since theoven walls and door walls generally consist of metal having good heatconductivity, these walls are heated at a considerably high temperaturedue to the heat from the energy source or the foodstuff when cooking isis progress. Therefore, in order to secure safety in entry andwithdrawal of the foodstuff from the oven compartment, thehandle-attached door as well as the oven walls must be kept at arelatively low temperature.

In conventional cooking apparatus, although the cooling unit for theoven walls is provided by establishing a passage for circulation of anair stream between the oven walls and the cabinet enclosing the ovenwalls, the cooling of the door is scarcely considered for variousreasons. Examples of the cooling unit are disclosed in U.S. Pat. Nos.3,081,392 and 3,339,054. The effective cooling of the door is essentialfor domestic use. In case of installing the cooling unit in or on thedoor which very often is moved to an open or a closed position, the doorconstruction becomes complicated and much more expensive than previousdesigns and further is inconvenient for the opening and closing of thedoor. In the prior art the cooling of the door is attained by naturallycooling or filling the interior of the door with a heat isolator andaccordingly the cooling power for the door is poor and the door will bedangerously heated to a considerably high temperature due to long,continuous use. In case of microwave oven wherein the foodstuff withinthe oven compartment is cooked by dielectric heating alone, metallicoven walls and door walls are heated a little due to the heat from thefoodstuff and the like, but are not heated to such a degree that theoperator might feel the heat around the door, and thus there is noparticular necessity of the door cooling unit. On the contrary, in caseof another microwave oven wherein a register type heater or a source ofhot blast is provided to produce browning or to speed up the cooking,the radiant heat from the heater, hot air and fumes cause the oven wallsand the door walls to be overheated. Of course, where such overheatingbecomes excessive, it causes damage to the operator in entering andwithdrawing of the foodstuff into the oven compartment.

During the cooking process oil or the other exhalation from thefoodstuff get scorched and stuck to the inner walls of the ovencompartment and the door. In the case where the inner walls areoverheated it is difficult to remove a stain on the inner wallstherefrom. However, in the case where the wall surface is properlycooled at a low temperature a stain on the inner walls could be easilyremoved by merely wiping ofi with a piece of cloth after the coolingprocess.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, the primary object ofthis invention is to provide an improved cooking apparatus wherein aforced-air cooling unit is adopted to cool effectively the interior ofthe door.

Another object of this invention is to provide an improved coolingapparatus which is provided with a cooling unit for making an air streampassing over the interior of the door circulating along the outersurface of the oven compartment thereby cooling the interior of the doorand the exterior of the oven compartment.

Still another objct of this invention is to provide an improved coolingapparatus having a simple blower unit for simultaneously exhausting anair stream for cooling the door and an air stream for the interior ofthe oven compartment.

A further object of this invention is to provide an improved cookingapparatus having an effective cooling unit suitable for microwave ovenwherein a resistor type heater or a source of hot blast is installed.

In summary, this invention refers primarily to improved coolingapparatus which comprises an enclosure having an access opening thereinto receive an article or other foodstuff to be heated, a door fitted tosaid enclosure to freely open and close said access opening and meansfor cooling the interior of said door. A blower means for effectivelycooling the door is designed to aspirate air from the surroundingambience and to exhaust air passing over the interior of the door to thesurrounding ambience. The door is provided with an outer wall having aplurality of apertures to permit the stream of air to be introduced intothe interior of the door and with inner wall having another aperture topermit the stream of air to escape from the interior of the door. In apreferred example, a microwave cooking apparatus comprises a metallicoven having an access opening therein to receive foodstuff to be cooked,a metallic door fitted to said oven to freely open and close said accessopening, means for supplying high frequency electromagnetic waves to theinterior of said oven, browning means for surface browning of foodstuffand cooling means for sending air to the interior of said door and theexterior of said oven thereby preventing the temperature rise of saiddoor and said oven due to the heat from said browning means.

Further details will be apparent from the following explanation ofexamples of embodiments of this invention with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view in verticalsection showing an oven structure of this invention.

FIG. 2 is a sectional view in vertical section showing anotherembodiment of this invention.

FIG. 3 is a sectional view in horizontal section showing still anotherembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,in FIG. 1, it will be seen that reference character 1 indicatesgenerally a cooking apparatus of the type disclosed in theaforementioned summary. The cooking apparatus 1 contains a metallicenclosure or oven compartment indicated by the numeral 2. The ovencompartment 2 may comprise a rectangular chamber having a top wall, abottom wall,

a front wall, a rear wall and side walls. A cabinet 3, or the like,encloses the oven compartment 2 in spaced relation to provide passagefor circulation of air stream against the oven compartment 2. Thepassage for air stream is established between the oven compartment 2 andthe cabinet 3 to permit air stream to pass therethrough. A resistor typeheater 4 as an energy source thereof is secured to the upper wall of theoven compartment 2 by a pair of rods extending through the upper walland the foodstuff or the like is treated by the heater 4. A metallicdoor 5 is pivotally affixed on the front of the oven compartment 2 tofreely open and close an access opening thereto, facilitating the entryand withdrawal of the foodstuff into the oven compartment 2. The door 5further has at the center thereof a window 6 permitting visualinspection of the contents of the oven compartment 2 and the window 6being covered with glass or the like secured to the door 5. A latchmechanism having a handle 7 maintains the door 5 in its upper or closedposition.

In addition, it will be noted that the door 5 is a hollow frame havingan inner wall 8 and an outer wall 9. One end of the outer wall 9 facesthe periphery of the window 6 in spaced relation against the peripheryto provide a first aperture 10 defining an inhale end for a passage ofan air stream through the interior of the door 5. That is, the firstaperture 10 is located around the entire periphery of the window 6. Aportion of the inner wall 8 is cut to provide a second aperture 11defining an exhaust end for the passage of an air stream through thedoor 5. The peripheral end of the front wall of the oven compartment 2also is cut to provide a third aperture 12 between the front end of theoven compartment 2 and that of the cabinet 3. The third aperture 12defines an inhale end for a passage of an air stream through theexterior of the oven compartment 2. The third aperture 12 is disposed inthe front wall of the oven compartment 2 at a location corresponding tothe second aperture 11 in the inner wall 8 of the door frame in itsclosed position and accordingly the passage of an air stream through theinterior of the door 5 communicates with that through the exterior ofthe oven compartment 2. Moreover, the upper portion of the cabinet 3 iscut to provide a fourth aperture 13 defining an exhaust end for thepassage of an air stream through theexterior of the oven compartment 2.A blower unit 14 having a motor and fan blades is provided near thefourth aperture or exhaust end 13.

In operation of the oven, the foodstuff is placed in the ovencompartment 2 and is heated by the radiant heat from the resistor heater4. During the cooking operation the blower unit 14 serves tosimultaneously cool the interior of the door 5 and the exterior of theoven compartment 2. The first, second, third and fourth apertures 10,11, 12, 13 are in the path of stream of air caused to flow by the blowerunit 14. The air moved by the fan blades therefore flows into the door 5through the aperture 10, and moves along the inside face of the door 5and into the exterior of the oven compartment 2 through the alignedapertures 11 and 12. Cooling the interior of the door 5, the air streamis permitted to escape from the exterior of the oven compartment 2through the aperture 13.

The'abovementioned cooling means is an important feature of thisinvention and permits the interior of the door, as well as the exteriorof the oven compartment, to cool simultaneously and thus prevents thewalls of the door and the oven compartment and various electricalcomponents positioned within the cabinet from being overheated. Thus, asafety feature is effected whereby injury is prevented to an operator.Furthermore, the cooling of the oven walls and the door is attained by asingle blower, and more particularly the cooling of the door is attainedonly by hollow door construction having at least one pair of aperturesdefining the path of an air stream therethrough.

Turning now to FIG. 2 of the drawings, there is illustrated a device forintroducing microwave energy to the enclosure or oven compartment 21 forheating the foodstuff therein which is preferably a magnetron 22. Themagnetron 22 is disposed between the oven compartment 21 and the cabinet23 enclosing the oven compartment 21, and is connected with one end ofthe wave guide 24 with an antenna or a coaxial output connector. Thus,the foodstuff within the oven compartment 21 is cooked by dielectricheating induced by high frequency microwaves which are introduced intothe oven compartment through the wave guide 24.

A metallic stirrer fan 25 is rotatably suspended from the upper wall ofthe oven compartment 21. The function of the stirrer fan 25 is to spreadthe radiant energy passing through the wave guide 24 substantiallyevenly around the periphery of the interior of the oven. The stirrer fan25 is driven by a motor 26. Furthermore, a resistor type heater 27 issuspended from the upper wall of the oven compartment 21 and arranged tobrown the surface of the foodstuff within the oven compartment 21 bymeans of the radiant heat therefrom. The browning means 27 is enclosedwithin a covering 28 of wire net or the like, which is operative toshield the browning means 21 from the microwave electric fields.

A hinge (not shown) is secured to a portion of the cabinet 23 and to adoor 29 to permit the door 29 to be selectively opened and closed tofacilitate the entry and withdrawal of the foodstuff into the ovencompartment 21. The door 29 is a hollow frame having an inner wall 30and an outer wall 31 and further having a window 32 permitting visualinspection of the contents of the oven compartment 21. The inner wall 30consists of a metallic sheet, and at least a portion thereofcorresponding to the window 32 is punched or perforatedin a manner toprevent radiation from escaping from the oven compartment 21 through thewindow 32 and further is covered with a screen glass 33 which serves toprevent cooking odors and other vapors created during the cookingprocess to be expelled through the window 32. A second screen glass 34is fitted to the outer wall 31 of the door 29 at a locationcorresponding to the above screen glass 33 by means of a supportingframe 34 having a L-shape section.

The supporting frame 34 has a plurality of holes 36 to aspirate air fromthe surrounding ambience. The inside periphery of the outer wall 31 alsohas a plurality of first apertures 37 cooperating with the holes 36 anddefining an inhale end for the path of an air stream through theinterior of the door 29. Moreover, the outside periphery of the innerwall 30 of the door 29 is cut to provide a second aperture 38 definingan exhaust end for the path of an air stream through the interior of thedoor 29. The second aperture 38 communicates with a third aperture 39defining an inhale end for the path between the oven compartment 21 andthe cabinet 23. A rear wall of the cabinet 23 is provided with aplurality of fourth apertures 40 defining an exhaust end for the pathbetween the oven compartment 21 and the cabinet 23. A blower unit 41having a motor and fan blades is supported in front of the fourthappertures 40.

An ornamental panel 42 is secured to the flange end of the ovencompartment 21 in spaced relation against the periphery of the doorconstruction and is provided with a fifth aperture 43 defining anotherinhale end for the path of an air stream through the exterior of theoven compartment 21. The bottom wall of the cabinet 23 also is providedwith a plurality of sixth apertures 44 defining further another inhaleend for the path of an air stream. A handle 45 is secured to the outeror front wall of the door 29.

The blower unit 41 is actuated during the cooking process. The air movedby the blower 41 flows through the interior of the door 29 through theapertures 36, 37, and moves air along the door walls 30, 31 and into theexterior of the oven compartment 21 through the aligned apertures 38,39. The outside air also is drawn into the exterior of the ovencompartment 21 through the space between the ornamental frame 42 and theperiphery of the door 29, the aperture 43 within the ornamental frame 42and the aperture 44 in the bottom wall. The air streams A, B, C flowtogether along the oven walls, cooling simultaneously the interior ofthe door 29 and the exterior of the oven compartment 21. The air streamsA, B, C and D are permitted to escape from the exterior of the ovencompartment 21 through the rear apertures 40, which is closed by anoverlapping screen 46 blocking the escape of microwave energy therefrom.In the case where the foodstuff is heated by dielectric heating alone,the blower 41 may be stopped.

It will be noted that the door 29 is provided with a seal or metalliccontact 47 for preventing the egress of microwave energy from the ovencompartment 21. The top'and bottom of the door 29 extend beyond the sealmeans 47 between the door 29 and the entrance to the oven compartment 21for assuring that there is no escape of the microwave energy. Theapertures 37 are sufficiently small as to prevent any radiation whichmanages to leak between the door 29 and the entrance to the ovencompartment 21.

The magnetron 22 is preferably of the air-cooled type having a pluralityof tins, and a stream of cooling air E is forced past the radiating finsby a blower unit 48 having a motor and fan blades through a duct 49. Thecooling unit 48 cools the magnetron 22 and ventilates the interior ofthe oven compartment 21, thereby preventing build-up of undesirablecondensation in the oven compartment 21.

In FIG. 3 there is illustrated another type of a microwave oven whereina hot air blast source is provided for surface browning of thefoodstuff. The hot blast type browning means 50 generally comprisesfanblades 51, a motor 52, a heater 53 and a duct 54. The one end of theduct 54 is connected to the side wall of the oven compartment 21 and theother end thereof being connected to the rear wall of the ovencompartment 21 and thereby establishing the circulation path for an airstream. The browning means 50 aspirates air from the oven compartment 21and the air stream flows along the duct 50 and then is heated by theheater 53 to pro duce hot air for surface browning. At this time thecooling air stream passing over the interior of the door 29 coolseffectively the browning unit 50 as well as the oven walls.

The aperture 38 in the door 29 may be provided with gasket member 55substantially impervious to microwave energy and capable of transmittingthe cooling air. Otherwise, the inhale end for the cooling air path isprovided with 1/4 wavelength choke 56.

Although the description of this invention has been made with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example and that numerous changes in thedetails of construction and the combination and arrangement of the partsand elements may be resorted to without departing from the spirit andscope of this invention.

I claim:

1. A heating apparatus comprising an enclosure having an access openingtherein to receive an article to be heated, a cabinet surrounding saidenclosure in spaced relation thereto having an opening adjacent saidaccess opening and having an exhaust opening, a hollow frame door havingan outer wall and an inner wall fitted to said enclosure to freely openand close said access opening, said inner wall having a centrallylocated area having multiple perforations, a window overlying saidcentrally located perforated area, said outer wall having a centrallylocated opening in spaced relation with said window, an exhaust aperturenear the periphery of said inner wall, an air flow path defined by saidcentrally located opening in said outer wall, the interior of saidhollow door, said exhaust aperture near the periphery of said inner wallin communication with said space between said cabinet and enclosure whensaid door is closed, and said exhaust opening in said cabinet, a sourceof high frequency electro magnetic waves in communication with theinterior of said enclosure, a metal to metal seal between said door andsaid enclosure to seal against energy loss from said enclosure throughsaid access opening, and a fan disposed in said exhaust opening in saidcabinet for moving air along said air flow path 2. A heating apparatusas in claim 2 together with an additional window disposed in saidcentrally located opening in said outer wall, said outer wall having aplurality of openings surrounding said additional window incommunication with the interior of said hollow door for providing saidcentrally located opening in said outer wall.

3. A microwave cooking apparatus comprising a metallic oven having anaccess opening therein to receive the foodstuff to be cooked, a cabinetsurrounding said oven in spaced relation thereto having an accessopening overlying said access opening in said oven and having an exhaustopening, a hollow metallic door having an inner and outer wall in spacedrelation fitted to said enclosure to freely open and close said accessopening, said inner wall having a perforated area centrally locatedwhich bars microwave energy, said outer wall having a centrally locatedopening in juxtaposition with said perforated area, a screen glassmember secured overlying said perforated area for barring cookingvapors, a plurality of outlet apertures through the periphery of saidinner wall, a source of high frequency electromagnetic waves incommunication with the interior of said oven, a metal to metal sealbetween said door and said oven surrounding said access opening to sealagainst energy loss from said oven through said access opening, radiantheating means for surface browning of the food stuffs, an air flow pathextending from said centrally located opening in said door through theinterior of said door through the outlet apertures at the periphery ofsaid door into the space between said oven and said cabinet and throughsaid exhaust aperture in said cabinet, and a blower for moving coolingair through said air flow path, said blower serving to preventtemperature rise of said outer wall due to the heat from said radiantheating means.

4. A microwave cooking apparatus comprising a metallic oven having anaccess opening therein to receive the foodstuff to be cooked, a cabinetsurrounding said oven in spaced relation thereto having a front accessopening overlying said access opening in said oven and an exhaustopening, a hollow metallic door having an inner wall and an outer wallfitted to said oven to freely open and close said access opening, saidinner wall having a perforated area centrally located which barsmicrowave energy, said outer wall having a centrally located windowopening overlying said perforated area in said inner wall, first andsecond screen glass members secured overlying said perforated area insaid inner wall and said opening in said outer wall respectively forbarring cooking vapors, a plurality of inlet apertures surrounding saidsecond screen glass in communication with the interior of said door, aplurality of exhaust apertures through the periphery of said inner wall,a source of high frequency electromagnetic waves in communication withthe interior of said oven, browning means for surface browning of thefoodstuff, an airflow path defined by said inlet apertures in saidhollow door, the interior of said door, said exhaust apertures in saiddoor, said space between said oven and said cabinet, and said exhaustaperture in said cabinet, a metal to metal seal between said door andsaid oven to seal against energy loss from said oven through said accessopening, a seal mounted in said exhaust apertures in said hollow doorsubstantially impervious to microwave energy and capable of transmittingair, and a fan disposed in said exhaust aperture in said cabinet formoving air through said air flow path, thereby cooling said outer wallof said hollow door and said cabinet.

1. A heating apparatus comprising an enclosure having an access openingtherein to receive an article to be heated, a cabinet surrounding saidenclosure in spaced relation thereto having an opening adjacent saidaccess opening and having an exhaust opening, a hollow frame door havingan outer wall and an inner wall fitted to said enclosure to freely openand close said access opening, said inner wall having a centrallylocated area having multiple perforations, a window overlying saidcentrally located perforated area, said outer wall having a centrallylocated opening in spaced relation with said window, an exhaust aperturenear the periphery of said inner wall, an air flow path defined by saidcentrally located opening in said outer wall, the interior of saidhollow door, said exhaust aperture near the periphery of said inner wallin communication with said space between said cabinet and enclosure whensaid door is closed, and said exhaust opening In said cabinet, a sourceof high frequency electro magnetic waves in communication with theinterior of said enclosure, a metal to metal seal between said door andsaid enclosure to seal against energy loss from said enclosure throughsaid access opening, and a fan disposed in said exhaust opening in saidcabinet for moving air along said air flow path
 2. A heating apparatusas in claim 2 together with an additional window disposed in saidcentrally located opening in said outer wall, said outer wall having aplurality of openings surrounding said additional window incommunication with the interior of said hollow door for providing saidcentrally located opening in said outer wall.
 3. A microwave cookingapparatus comprising a metallic oven having an access opening therein toreceive the foodstuff to be cooked, a cabinet surrounding said oven inspaced relation thereto having an access opening overlying said accessopening in said oven and having an exhaust opening, a hollow metallicdoor having an inner and outer wall in spaced relation fitted to saidenclosure to freely open and close said access opening, said inner wallhaving a perforated area centrally located which bars microwave energy,said outer wall having a centrally located opening in juxtaposition withsaid perforated area, a screen glass member secured overlying saidperforated area for barring cooking vapors, a plurality of outletapertures through the periphery of said inner wall, a source of highfrequency electromagnetic waves in communication with the interior ofsaid oven, a metal to metal seal between said door and said ovensurrounding said access opening to seal against energy loss from saidoven through said access opening, radiant heating means for surfacebrowning of the food stuffs, an air flow path extending from saidcentrally located opening in said door through the interior of said doorthrough the outlet apertures at the periphery of said door into thespace between said oven and said cabinet and through said exhaustaperture in said cabinet, and a blower for moving cooling air throughsaid air flow path, said blower serving to prevent temperature rise ofsaid outer wall due to the heat from said radiant heating means.
 4. Amicrowave cooking apparatus comprising a metallic oven having an accessopening therein to receive the foodstuff to be cooked, a cabinetsurrounding said oven in spaced relation thereto having a front accessopening overlying said access opening in said oven and an exhaustopening, a hollow metallic door having an inner wall and an outer wallfitted to said oven to freely open and close said access opening, saidinner wall having a perforated area centrally located which barsmicrowave energy, said outer wall having a centrally located windowopening overlying said perforated area in said inner wall, first andsecond screen glass members secured overlying said perforated area insaid inner wall and said opening in said outer wall respectively forbarring cooking vapors, a plurality of inlet apertures surrounding saidsecond screen glass in communication with the interior of said door, aplurality of exhaust apertures through the periphery of said inner wall,a source of high frequency electromagnetic waves in communication withthe interior of said oven, browning means for surface browning of thefoodstuff, an airflow path defined by said inlet apertures in saidhollow door, the interior of said door, said exhaust apertures in saiddoor, said space between said oven and said cabinet, and said exhaustaperture in said cabinet, a metal to metal seal between said door andsaid oven to seal against energy loss from said oven through said accessopening, a seal mounted in said exhaust apertures in said hollow doorsubstantially impervious to microwave energy and capable of transmittingair, and a fan disposed in said exhaust aperture in said cabinet formoving air through said air flow path, thereby cooling said outer wallof said hollow door and said cabinet.